In the water supply system, vacuum-type situations can easily occur due to water supply cutoff or many other reasons. Additionally, when the pressure is lower than the atmospheric pressure, the result may be siphon and liquid reflux. When the siphon and liquid reflux is serious, it can pollute the whole water supply system. Currently, to achieve the anti-siphon effect and to prevent the system from leaking, some reflux devices use a unidirectional valve to activate a diaphragm for sealing the air inlet. However, this may result in a considerable loss in the current pressure of the system. The present invention helps to solve the problem of current pressure loss, and realizes an effective anti-siphon effect.